April 15, 2012 -- An experimental drug called florbetaben may help doctors diagnose Alzheimer's disease earlier in some people with memory problems.

Florbetaben is one of several new radioactive drugs being used to detect Alzheimer's disease. Others include Amyvid, approved last week by the FDA.

After florbetaben is injected, the amyloid plaques in the brain that are a hallmark of Alzheimer's disease light up on a brain imaging scan called positron emission tomography (PET), says Marwan Sabbagh, MD, director of Banner Sun Health Research Institute in Sun City, Ariz.

In late-stage testing, Sabbagh and colleagues compared PET scans using florbetaben taken from 31 people in the months before they died to brain tissue taken in autopsies. The presence of plaques at autopsy is currently the only way to confirm a diagnosis of Alzheimer's.

The scans correctly identified 100% of people who had plaques at autopsy, but one person who tested positive for plaques did not end up having any -- a small dent in the test?s accuracy.

The findings are scheduled to be presented next week at the annual meeting of the American Academy of Neurology in New Orleans.

Limitations of Testing

By themselves, florbetaben and its cousins will not pinpoint people with Alzheimer's. What they can do is provide skilled doctors one more piece of information that can be used either to make a diagnosis of Alzheimer's -- or rule it out, experts say.

That's because the scans detect amyloid plaque in the brain, not Alzheimer's itself. Although people with Alzheimer's always have amyloid plaque, plaque does mean someone has Alzheimer's.

For people with memory problems, disorientation, and other symptoms of Alzheimer's, a positive scan means there is a "high probability of Alzheimer's or that Alzheimer's is contributing to the patient's [memory problems]," Sabbagh tells WebMD.

A negative scan in a person with symptoms means the probability of Alzheimer's is extremely low, he says.

The most important thing to know about the new tests is that they only should be performed by a skilled doctor with experience in diagnosing Alzheimer's, says Rachelle S. Doody, MD, PhD, director of the Alzheimer's Disease and Memory Disorders Center at Baylor College of Medicine in Houston.

"A diagnosis of Alzheimer's requires lots of bits of information. This is not a revolution for the diagnosis of Alzheimer's but one of those bits of information that can be helpful," says Doody, who was not involved with the work.

The tests should not be performed in people who do not have memory problems or other symptoms of Alzheimer's, she tells WebMD.

Pros, Cons of Testing

Some experts question the usefulness of any test, since no drugs are available that substantially halt the course of Alzheimer's.

Sabbagh says available medications can help somewhat. But more importantly, drugs that can slow the progression of the disease are in late-stage testing. Once they become available, the tests could help doctors select patients for early treatment, when it can really help, he says.

Pros, Cons of Testing

Some experts question the usefulness of any test, though, since no drugs are available that substantially halt the course of the progressive disease.

Sabbagh says that medications already out there can help somewhat. But more importantly, drugs that can slow the progression of the disease are in late-stage testing. Once they become available, the tests could help doctors select patients for early treatment, when it can really help, he says.

Additionally, a diagnosis can help families in planning and in creating plans to help protect the patient, Doody says.

Another question is whether doctors can read scan results accurately and consistently. Eli Lilly has established a program to train doctors to interpret the results for its drug, Amyvid, and the manufacturers of the other agents, if approved, will presumably do the same.

There are potential pluses, too.

If the tests can help to identify people with Alzheimer's earlier, that will likely advance research, experts say. Some believe that the reason experimental drugs have failed to work up to now is because they have been tested in people whose disease was too advanced.

Florbetaben Details

Florbetaben and other new drugs like it have not been compared in a head-to-head study so no one knows which works best.

But one advantage of florbetaben may be that it appears to last relatively long before it loses its radioactivity, Sabbagh says. That means it can be shipped and used at centers worldwide, while some imaging agents can only be used at the institution where they are made.

Also, the researchers took the extra step of making sure florbetaben detects amyloid in the areas of the brain it is supposed to -- the gray matter, he says.

The most common side effects were discomfort and bruising in the area where the drug is injected, headache, and flushing. But symptoms were short-lived, Sabbagh says.

The study was funded by maker Bayer Healthcare Berlin, which plans to submit the results with an application for FDA approval.

No cost has been established for florbetaben. Amyvid is estimated to cost $1,600 a dose, and a PET scan can run from $3,000 to $6,000. When Amyvid becomes available in June, Medicare and presumably most other insurers will not immediately cover its expense.

About 5.4 million people are living with Alzheimer's disease, and there are 15.2 million caregivers of people with Alzheimer's and other dementias, according to the Alzheimer's Association.

These findings were presented at a medical conference. They should be considered preliminary, as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.